Ordinary ordinary cooling fan voltage is 12 v, but some customers products, such as temperature control cooling fan, cooling fan voltage at low temperature setting lower at present, under the condition of the low voltage, cooling fan speed will be slower and quieter in three different levels of air volume, in order to design some customers design three kinds of different voltage of less than 12 v,  In this way, the cooling fan that does not work within the rated voltage range for a long time will not be damaged.  As long as the supplier can ensure the normal operation under low voltage, ensure the normal start and operation of ordinary 12V cooling fan, there is no problem below 12V, for example, 12V high-speed cooling fan can work under the voltage as low as 5V, even 4.5V, at this time the sound is relatively quiet.